There's a circle graph in the book, with more than half labelled as "boys" and measuring 240 degrees (or so), a nice-sized wedge labelled as "girls" and measuring 110 degrees (or so), and a tiny bit labelled "teachers" measuring about 10 degrees.

a) If the total population is 1,800, how many boys, girls, and teachers are there?b) If 2/5 of the girls are above 12 years old, what is the angle of the sector representing this?c) What percentage, rounded to the nearest per cent, of the students are boys?

For part (a), I think we should divide the degrees for that sector by the degrees for the whole circle, use this like "percent", and multiply this on the total population. So "boys" would be (240/360)(1800) = (2/3)(1800) = 1200.

For part (b), we should multiply the 550 girls by the 2/5 to get 220 under-12s. Then 220/1800 = 0.122... and (220/1800)(360 degrees) = 44 degrees, and this should be the size of the wedge.

For part (c), there are 1750 students and 1200 are boys, so we should do 1200/1750 = 0.68571428..., or about 69% (to the nearest whole percent).